WO2016001164A1

WO2016001164A1 - Process for purifying polycarbonate polyols and purifying apparatus therefor

Info

Publication number: WO2016001164A1
Application number: PCT/EP2015/064733
Authority: WO
Inventors: Jörg Hofmann; Stefanie Braun; Kai LAEMMERHOLD; Matthias Wohak; Cyrus Ahmadzade; Jürgen BAUSA
Original assignee: Covestro Deutschland Ag
Priority date: 2014-07-03
Filing date: 2015-06-29
Publication date: 2016-01-07
Also published as: CN106471041B; EP3164443A1; US10421836B2; EP3164443B1; KR102341197B1; ES2709474T3; US20170152345A1; CN106471041A; KR20170026555A; SG11201610898TA

Abstract

The present invention relates to a purifying apparatus for polycarbonate polyols, especially for removal of cyclic alkylene carbonates, comprising an evaporation unit (1) provided with a heater (10) and having an inlet (6) disposed at the top end thereof and a bottoms vessel (11), and a stripping column (2) connected downstream of the evaporation unit (1) and having a top (21) and a bottom (23), wherein a feed (5) for the polycarbonate polyol to be purified opens into the inlet (6) to the evaporation unit (1) and a gas outlet line (12) and a connecting line which opens into the top (21) of the stripping column (2) and is equipped with a pump (18) depart from the evaporation unit (1), and wherein a gas inlet line (24) for an inert gas opens into the bottom (23) of the stripping column (2) and a product line (27) for the purified polycarbonate polyol departs from the bottom (23) of the stripping column (2) and a gas outlet line (25) departs from the top (21) of the stripping column (2). The invention additionally relates to a process for purifying polycarbonate polyols with such a purifying apparatus.

Description

Process for the purification of polycarbonate polyols and cleaning device therefor

The present invention relates to a cleaning device for polycarbonate polyols, in particular for the separation of cyclic alkylene carbonates, and a method for operating such a device.

Polycarbonate polyols have become increasingly popular in recent years. Thus, these compounds can be used at least partially instead of polyether polyols, especially in the production of polyurethane foams, in particular flexible foams. Carbon dioxide is used as comonomer in polycarbonate polyols. This is not only less expensive than the alkylene oxides typically used for polyether polyols, such as ethylene oxide or propylene oxide, which are mostly petrochemical origin, but by the incorporation of carbon dioxide into the polymer is simultaneously used a greenhouse gas, which is environmentally interesting.

Processes for the preparation of polycarbonate polyols are known in principle. These are usually generated starting from a starter substance using suitable catalysts of alkylene oxides and carbon dioxide. Essentially, a distinction is made between two production methods. In the first variant, alkylene oxide units and the carbon dioxide used as a comonomer are built up to a large extent alternating with a polymer chain. As a starter for this reaction, a short-chain polyol, in particular a diol can be used, such as ethylene glycol. Such a manufacturing method is known for example from WO 2010/028362 AI.

Another manufacturing method is known for example from WO 2008/092767 AI. In this known preparation method, starting from a short-chain starter, such as ethylene glycol or glycerol, using so-called double metal cyanide catalysts (DMC catalysts), a polymer is constructed which, in addition to the carbonate groups composed of alkylene oxide and carbon dioxide, additionally contains ether groups in the polymer chain has. This is achieved in that DMC catalysts can catalyze not only the reaction of alkylene oxide with carbon dioxide, but equally the ether formation by reaction of two alkylene oxides with one another. As a result, the property profile of the polymers obtained can be adapted considerably more flexibly.

In the case of the abovementioned production processes, however, undesired side reactions typically occur in addition to the actual polymer chain structure, which lead to low-molecular-weight products. lead. For example, the reaction of a molecule-alkylene oxide with a molecular carbon dioxide can lead to the formation of cyclic alkylene carbonates, for example when propylene oxide is used to form propylene carbonate. The formation is shown in the following formula (I) (for example, R = CH 3 propylene carbonate):

Starter-OH +

Since the presence of these compounds in the end product is generally undesirable, the polymerization is carried out under conditions in which as little as possible cyclic alkylene carbonate is formed. This can be achieved in a conventional manner by adhering to certain reaction temperatures. This is described, for example, in WO 2008/092767, where the preferred reaction temperature is 80-130 ° C. Nevertheless, even by these measures, formation of cyclic alkylene carbonates can not be completely suppressed. For example, polyethercarbonate polyols prepared by DMC catalysis have a content of from 3 to 15% by weight of cyclic alkylene carbonate. The proportion of cyclic Alkylencarbonaten contained in the polycarbonate polyol is so far reduced after production by separation processes to a content of less than 1%.

WO 2008/092767 describes the separation of the cyclic propylene carbonate (cPC) by means of vacuum stripping at 150 ° C. (3 hours), cPC residual contents <200 ppm being obtained in the end product. In addition, the separation of cPC by means of a thin-film evaporator or falling-film evaporator in a high vacuum (pressure <1 mbar) at 120 ° C. (see BMS 11 1 160-EP, Application No. 12181907.7) is described. Residual contents of cPC are not specified here.

The object of the present invention was thus to provide an improved process for the purification of polycarbonate polyols which can be operated with a reduced apparatus design and at the same time enables a high purification performance, in particular with regard to the removal of cyclic alkylene carbonates. Furthermore, a corresponding cleaning device is to be provided with which this method can be performed.

The object is achieved by a cleaning device for polycarbonate polyols, in particular for the separation of cyclic alkylene carbonates, comprising an evaporation device provided with a heater with an inlet arranged at the top thereof and a sump and a stripping column with a head and a sump connected downstream of the evaporation device, wherein a feed line for the polycarbonate polyol to be purified opens into the inlet of the evaporation device and from the evaporation device a gas outlet line and a connection line opening into the top of the stripping column and equipped with a pump and wherein in the bottom of the stripping a gas inlet line for an inert gas opens and depart from the bottom of the stripping a product line for the purified polycarbonate and from the top of the stripping a gas outlet.

In the context of the present invention, the term "polycarbonatepolyols" is understood as a generic term which also includes polycarbonatepolyols which are not constructed in a purely alternating manner but also have ether units Such polycarbonatepolyols are also referred to as "polyethercarbonatepolyols". For the inventive cleaning method, the origin of the polycarbonate polyol to be purified is irrelevant. It may be a strictly alternating polycarbonate polyol, a polyethercarbonate polyol, or polycarbonate polyols prepared, for example, on a low molecular weight initiator such as e.g. Glycerol or a higher molecular weight starter, such as PEG 800 or other higher molecular weight starters based.

The invention is based on the finding that using a two-stage process in which the first stage is formed by an evaporation device and the second stage by a stripping column, at relatively easily realizable operating conditions, such as pressure and temperature, a large part of the impurities present are removed can, in particular the existing cyclic Alkylencarbonate.

Thus, the evaporation device can be operated, for example, at a pressure of 100 mbar or below, preferably at 5 to 100 mbar, preferably at 50 mbar or below, more preferably at 25 mbar or below, particularly preferably at 10 mbar or below, wherein the crude product fed is heated to a temperature of for example 120 to 180 ° C, preferably about 160 ° C. In this way, some of the volatile compounds, which include the cyclic alkylene, are removed by evaporation, which can then be condensed in a condenser. In this case, the specified operating pressure can be adjusted technically relatively easily, the operating temperatures on the other hand are still within a tolerable range, which does not have to be expected in a significant scale with a decomposition of the polycarbonate polyols. It is therefore not necessary in the method according to the invention to operate the evaporation device in a high vacuum. In addition, in the device according to the invention or the method according to the invention, the residence time in the evaporation device can be kept comparatively low, for example below one minute. Even in the bottom of the evaporation device, a be set for a short residence time of, for example, 15 minutes or less, preferably 3 minutes or less, so that even at this point the polycarbonate polyol is thermally not stressed too much.

However, it is also possible within the scope of the process according to the invention to set, for example, a residence time of 10 minutes to 2 hours in the bottom of the evaporation device. In this case, the bottom of the evaporator can be used as an intermediate buffer for the prepurified product. However, in particular with longer residence times, a replication of impurities can occur, such as, for example, cyclic alkylene carbonate. However, this replication takes place upstream of the stripping column in which the final purification is performed and is therefore less critical. Nevertheless, it is generally preferred within the scope of the process according to the invention to observe the abovementioned shorter residence times in the bottom of the evaporation device.

In the second stage, the product pre-cleaned by the evaporation device is fed to a stripping column, in which a further purification takes place. If cooling occurs in the feed line during the transfer of the prepurified product to the stripping column, it can be heated again to a temperature of, for example, 120 to 180.degree. C., in particular to about 160.degree. C., before being fed to the stripping column. The inert gas, for example nitrogen, fed into the bottom of the stripping column is typically likewise heated to the aforementioned temperature of from 120 to 180.degree. C., in particular to about 160.degree. As an alternative to nitrogen, carbon dioxide, water vapor or any desired mixture of the abovementioned fluids can also be used as the inert gas.

When nitrogen is used as the stripping gas, the specific nitrogen requirement is preferably in the range from 0.2 to 0.8 kg of nitrogen, more preferably in the range from 0.3 to 0.7 kg of nitrogen, in each case based on the mass (in kg). the product fed to the stripping column. Due to the fact that the product supplied to the stripping column is usually freed from most of the readily volatile compounds present, such as cyclic alkylene carbonates, the proportion evaporating in the stripping column is comparatively low, which only increases according to the enthalpy of vaporization to be applied a slight cooling of the stripping leads. Therefore, an additional heat supply to the stripping column is usually not required.

The stripping column can be operated in a vacuum, for example at a pressure of 50 to 150 mbar, in particular at about 80 mbar or under normal pressure. The inert gas stream loaded with volatile compounds, inter alia cyclic alkylene carbonate, can after leaving the stripping column are fed to one or more coolers, in which the volatile compounds are removed. The inert gas can then either be disposed of via the exhaust air or else compressed and returned to the process.

In the process according to the invention, the residence time in the stripping column can be kept comparatively short, for example less than 3 minutes, so that even in this second stage product damage is largely avoided.

In an advantageous embodiment of the cleaning device according to the invention, the gas outlet line of the evaporation device and / or the gas outlet line of the stripping column opens into a cooling device in which impurities transferred to the gaseous state and removed via the gas outlet line can be condensed, in particular cyclic alkylene carbonates. As a result, the volatile compounds can be removed, wherein, for example, the inert gas used in the stripping column can be returned to the process.

In the cleaning device can further be provided that the supply line, the connecting line, the gas inlet line and / or the product line are equipped with a heater. This is particularly advantageous in order to bring the fluid flow conveyed through these lines to the desired temperature or to reset the predetermined temperature when cooling has occurred below the desired operating temperature due to heat losses in the lines. In addition, by heating, the viscosity of the polymer delivered through the conduits is kept low. The heaters can be controlled independently of each other in such a manner that the conveyed in the respective lines fluid is heated to a temperature of 120 to 180 ° C, in particular to a temperature of about 160 ° C. Conveniently, the heater in the aforementioned lines is arranged in such a way that after passing through the heated area no significant cooling can be done before the heated to the desired temperature fluid is supplied to the next process stage.

According to a further embodiment of the cleaning device according to the invention, a three-way valve is arranged in the connecting line, from which an optionally provided with a heating and / or a pump return line, which opens into the supply line or into the inlet of the evaporation device. In other words, this creates a circulation line of the evaporator. This is particularly advantageous, since in this way a partial recycling of the prepurified product to the inlet of the evaporation device can be accomplished, whereby the concentration content of volatile compounds, such as cyclic alkylene carbonates, is reduced at the inlet of the evaporator. By repeatedly passing through the evaporation device whose separation efficiency is improved without having to increase the evaporation device in itself.

Analogously thereto, in the cleaning device according to the invention, a three-way valve may also be arranged in the product line, from which a return line provided, if desired, with a heating and / or a pump discharges into the evaporation device, in particular into the bottom of the evaporation device. This is particularly advantageous, because in this way the stripping column is passed through several times for a partial flow of the product to be purified. In addition, in particular when starting the cleaning device according to the invention, the product stream passing through the stripping column can be completely fed via the return line of the evaporation device until the plant is stabilized in such a way that the desired maximum values of impurities in the cleaned product are reached or undershot. For this purpose, in particular in the product line upstream of the three-way valve, a sampling point or a measuring station can be provided, with which the content of impurities to be removed can be determined. The content of cyclic alkylene carbonates can be determined, for example, by 'H-NMR. This method is explained in detail in the example section.

To generate the desired circulation, one or more pumps may be provided in the cleaning device, for example in the supply line and / or the product line. In principle, any device known to those skilled in the art can be used as evaporation device for the cleaning device according to the invention. For example, natural circulation, forced circulation, falling film, thin layer or Kettle evaporators are used, of which falling film and thin film evaporators are particularly preferred. It can further be provided that the supply line opens into the inlet of the evaporation device and the connecting line and the gas outlet line depart from the bottom of the evaporation device.

The evaporation device may be coupled to a vacuum device, which is in particular designed such that the evaporation device can be operated at a pressure of 100 mbar or below, preferably at 5 to 100 mbar, preferably at 50 mbar or below, more preferably at 25 mbar or below, more preferably at 10 mbar or below. This is particularly advantageous because the aforementioned operating pressures at the aforementioned operating temperatures of, for example, 120 to 180 ° C allow a good separation of the volatile constituents, at the same time excessive thermal stress on the product to be cleaned is prevented. The stripping column can be operated under atmospheric pressure or else in vacuo. In the last-mentioned embodiment, the stripping column is expediently coupled to a vacuum device, which is in particular designed such that a pressure of 150 mbar or below can be set in the top of the stripping column, preferably 100 mbar or below, preferably 80 mbar or below. The operation of the stripping column at these pressures and a temperature of for example 120 to 180 ° C allows a good separation of still existing volatile compounds, such as cyclic alkylene, at the same time at typical operating temperatures of 120 to 180 ° C too high a thermal load of the to be cleaned Product is avoided. In the case of the cleaning device according to the invention, even in the first stage, ie the evaporation device, a substantial proportion of the readily volatile compounds can be removed from the product to be purified, so that only a small proportion of readily volatile compounds must be removed in the stripping column. This leads to a comparatively low cooling of the stripping column. Frequently, it then suffices to heat the inert gas stream and to heat the prepurified product fed to the stripping column in order to keep the stripping column at the desired operating temperature. Nevertheless, it is also possible to provide the stripping column with a heating jacket, thereby enabling a substantially adiabatic operation. For this purpose, the heating jacket is expediently coupled via a control device with one or more temperature sensors which determine the operating temperature of the stripping column at various points and regulate the heating power of the heating jacket accordingly. In this case, the heating mantle can also be subdivided into a plurality of independently controllable zones in order to be able to set the desired temperature over the entire separation length of the stripping column.

The stripping column is advantageously filled with random packings and / or packings and / or equipped with trays. In this case, so-called Raschig super-rings are preferably used as packing.

A further subject matter of the present invention relates to a process for the purification of polycarbonate polyols with a purification device comprising a heating device with an inlet arranged at the top and a sump and a stripping column with a head and a sump connected downstream with the evaporation device, in particular with a cleaning device according to the invention, the method comprising the following steps: a) feeding the polycarbonate polyol to be purified into the inlet of the evaporation device through a feed line opening into it; b) in the evaporator overpasses a portion of the impurities in the gas phase and removing the gaseous impurities via a gas outlet, wherein in the bottom of the evaporator, a partially purified polycarbonate polyol is obtained; c) transferring the partially purified polycarbonate polyol from the bottom of the evaporation device into the top of the stripping column through a connection line opening into the latter, in particular by means of a pump; d) removing a further portion of the contaminants from the partially purified polycarbonate polyol by stripping in countercurrent flow through an inert gas stream introduced into the bottom of the stripping column via a gas inlet conduit and opposite the flow direction of the polycarbonate polyol, the contaminants being transferred to the gas phase and transported with the inert gas stream; e) discharging the impurities with the inert gas through a gas outlet conduit going from the top of the stripping column; f) removing the purified polycarbonate polyol via a product line leaving the bottom of the stripping column.

In an advantageous embodiment of the method according to the invention, nitrogen, carbon dioxide and / or water vapor can be used as the inert gas. As already stated above, the impurities to be removed in the process according to the invention include in particular cyclic alkylene carbonates, preferably cyclic propylene carbonate.

When nitrogen is used as the stripping gas, the specific nitrogen requirement is preferably in the range from 0.2 to 0.8 kg of nitrogen, more preferably in the range from 0.3 to 0.7 kg of nitrogen, in each case based on the mass (in kg). the stripping column supplied partially purified polycarbonate polyol. In an advantageous embodiment of the process according to the invention, the proportion of cyclic alkylene carbonates in the purified polycarbonate polyol is less than 100 ppm. This can be achieved, for example, by using three-way valves in the connecting line and / or the product line to return part of the prepurified product to the cleaning process and subject it to a new purification until the desired maximum value of 100 ppm of cyclic alkylene carbonates in the polycarbonate polyol is reached , In the method according to the invention it is furthermore advantageous that phosphoric acid is added to the polycarbonate polyol to be purified before or during the purification, in particular in a concentration of 10 to 1000 ppm, based on the polycarbonate polyol to be purified, in particular 15 to 500 ppm. For this purpose, for example, a feed for phosphoric acid can be provided in the supply line to the evaporation device. This is particularly advantageous because stabilization of the polycarbonate polyol is achieved by the addition of phosphoric acid, whereby a replication of cyclic alkylene carbonates is reduced within the cleaning device. The replication can be achieved by the fact that at elevated temperatures during the purification in the presence of catalyst traces contained in the product, for example a DMC catalyst, a so-called "back-biting" effect occurs, in which particular at the chain ends of the linear polycarbonate polyol individual Chain members are cleaved off, which in turn can then react to form cyclic alkylene carbonates.

In a first embodiment, the invention thus relates to a cleaning device for polycarbonate polyols, in particular for separating cyclic alkylene carbonates, comprising an evaporation device (1) provided with a heater (10) with an inlet (6) arranged on its top side and a sump (11). and a stripping column (2) connected downstream to the evaporation device (1) with a head (21) and a sump (23), wherein a feed line (5) for the polycarbonate polyol to be purified opens into the inlet (6) of the evaporation device (1) and leaving from the evaporation device (1) a gas outlet line (12) and a connecting line opening into the head (21) of the stripping column (2) and equipped with a pump (18), and into the sump (23) of the stripping column (2) a gas inlet line (24) for an inert gas and from the bottom (23) of the stripping column (2) a product line (27) for the purified polycarbonate polyol and from the head ( 21) of the stripping column (2) leave a gas outlet line (25).

In a second embodiment, the invention relates to a cleaning device according to the first embodiment, characterized in that the gas outlet line (12) of the evaporation device (1) and / or the gas outlet line (25) of the stripping column (2) each open into a cooling device (13), in which impurities converted into the gaseous state and removed via the gas outlet line (12, 25) can be condensed, in particular cyclic alkylene carbonates.

In a third embodiment, the invention relates to a cleaning device according to the first or second embodiment, characterized in that the supply line (5), the connection supply line (3), the gas inlet line (24) and / or the product line (27) are equipped with a heater (9).

In a fourth embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 3, characterized in that in the connecting line (3) a three-way valve (16) is arranged, of which a if desired with a heater (9) and / or a pump (18) provided return line (17), which opens into the supply line (5) or in the inlet (6) of the evaporation device (1).

In a fifth embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 4, characterized in that in the product line (27) a three-way valve (30) is arranged, of which, if desired, with a heater (9) and / or a return line (31) provided with a pump (18) discharges into the evaporation device (1), in particular into the sump (11) of the evaporation device (1).

In a sixth embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 5, characterized in that in the supply line (5) and / or the product line (27), a pump (18) is provided.

In a seventh embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 6, characterized in that the evaporation device (1) as natural circulation, forced circulation, falling film, thin-film or Kettle- evaporator is designed, preferably as a falling film or Thin-film evaporator, wherein the feed line (5) opens into the inlet (6) of the evaporation device (1) and the connecting line (3) and the gas outlet line (12) depart from the sump (11) of the evaporation device (1).

In an eighth embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 7, characterized in that the evaporation device (1) is coupled to a vacuum device, which is in particular designed such that the evaporation device (1) at a pressure of 100 mbar or less, preferably at 5 to 100 mbar, preferably at 50 mbar or below, more preferably at 25 mbar or below, particularly preferably at 10 mbar or below.

In a ninth embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 8, characterized in that the stripping column (2) is coupled to a negative pressure device, which is in particular designed such that in the head (21) of the stripping column ( 2) a pressure of 150 mbar or below can be set, preferably 100 mbar or below, preferably 80 mbar or below. In a tenth embodiment, the invention relates to a cleaning device according to one of embodiments 1 to 9, characterized in that the stripping column (2) is provided with a heating jacket (22), which allows a substantially adiabatic operation of the stripping column (2).

In an eleventh embodiment, the invention relates to a cleaning device according to one of the embodiments 1 to 10, characterized in that the stripping column (2) filled with packing and / or packings and / or is equipped with trays, in particular Raschig super-rings used as packing are.

In a twelfth embodiment, the invention relates to a process for purifying polycarbonate polyols with a cleaning device comprising an evaporation device (1) provided with a heater (10) with an inlet (6) arranged on its top side and a sump (11) and one with stripping column (2) connected downstream of the evaporation device (1) with a head (21) and a sump (23), in particular with a cleaning device according to one of claims 1 to 11, the method comprising the following steps: a) feeding the object to be cleaned Polycarbonatepolyols in the inlet (6) of the evaporation device (1) through an opening into this supply line (5); b) in the evaporation device (1) transferring part of the impurities into the gas phase and removing the gaseous impurities via a gas outlet line (12), wherein in the bottom (11) of the evaporation device (1) a partially purified polycarbonate polyol is obtained; c) transferring the partially purified polycarbonate polyol from the sump (11) of the evaporation device (1) into the head (21) of the stripping column (2) through a connecting line (3) opening into it, in particular by means of a pump (18); d) removing a further portion of the impurities from the partially purified polycarbonate polyol by stripping in countercurrent flow through an inert gas stream introduced into the bottom (23) of the stripping column (2) via a gas inlet line (24) and opposite the flow direction of the polycarbonate polyol, the impurities transferred to the gas phase and transported with the inert gas stream; e) discharging the impurities with the inert gas through a gas outlet pipe (25) emerging from the head (21) of the stripping column (2); f) discharging the purified polycarbonate polyol via a product line (27) leaving the sump (23) of the stripping column (2).

In a thirteenth embodiment, the invention relates to a method according to the twelfth embodiment, characterized in that nitrogen, carbon dioxide and / or water vapor is used as the inert gas.

In a fourteenth embodiment, the invention relates to a process according to one of the embodiments 12 or 13, characterized in that the impurities to be removed comprise cyclic alkylene carbonates, in particular cyclic propylene carbonate, wherein the proportion of cyclic alkylene carbonates in the purified polycarbonate polyol is preferably less than 100 ppm.

In a fifteenth embodiment, the invention relates to a method according to any one of embodiments 12 to 14, characterized in that phosphoric acid is added to the polycarbonate polyol to be purified before or during the purification, in particular in a concentration of 10 to 1000 ppm, based on the polycarbonate polyol to be purified , in particular 15 to 500 ppm.

The present invention will be explained in more detail below with reference to a figure and exemplary embodiments. The only one shows

Fig. 1 shows a schematic structure of a cleaning device according to the invention.

FIG. 1 shows an embodiment of a cleaning device for polycarbonate polyols according to the invention. The cleaning device serves to separate cyclic alkylene carbonates from polycarbonate polyols, in this case polyether carbonate polyols, which have been produced by means of DMC catalysis. The cleaning device consists essentially of an evaporation device 1, which is designed here as a falling film evaporator, and a stripping column 2 arranged downstream of the evaporation device 1. The evaporation device 1 and the stripping column 2 are connected to one another via a connecting line 3. The cleaning device is supplied to the polyether carbonate polyol to be purified from a heated drum 4 via a feed line 5, which opens into an inlet 6 of the evaporation device 1. The barrel 4 is also equipped with a ventilation 7. In the supply line 5 shut-off valves 8 and a heater 9 are provided. The evaporation device 1 has a heater 10 designed as a heating jacket with an inlet 10a and a drain 1 Ob for a heating fluid. The evaporation device 1 has at its lower end a sump 11, wherein above the sump 11 a gas outlet line 12 is provided for gaseous cyclic propylene carbonate, in which two sequentially connected cooler 13 are arranged, in which the cyclic propylene carbonate is condensed, wherein the liquid effluent for the condensed cyclic propylene carbonate opens ter 14 in a collecting container. Non-condensable components are removed via a downstream of the cooler 13 arranged exhaust system 15.

Below the sump 11, the connecting line 3 is connected, in which a three-way valve 16 is positioned, via which part of the prepurified product via a return line 17 to the inlet 6 of the evaporation device 1 can be returned. For positive displacement of the pre-cleaned product 17 pumps 18 are provided in the connecting line 3 and in the return line. In addition, the connecting line 3 has a sampling point 19, at which the content of impurities in the product stream can be determined. The connecting line 3 is further equipped with a heater 9 and a heat exchanger 20, by means of which the polyether carbonate polyol pre-purified in the evaporation device 1 can be kept at the desired temperature or brought to it. The stripping column 2 has a head 21, into which the connecting line 3 opens. The stripping column 2 is designed as a glass column DN80 with 8 m length, filled with Raschig Super-rings # 0.3 as filler and provided with separately controllable heating jackets 22, which with the aid of temperature sensors 22a coupled via a temperature control and not shown here allow essentially adiabatic operation of the stripping column 2. The effective separation length of the glass column of 8 m is divided into a 6 m long section in the upper section and into a 2 m section in the lower section, a sampling point 19 being provided between the sections.

The stripping column 2 further has a sump 23, above which a gas inlet line 24 for inert gas is connected, via which heatable inert gas, present nitrogen, can be fed into the stripping column 2 by means of a heat exchanger 20 so that it can be operated in countercurrent flow. To the head 21 of the stripping column 2, a gas outlet line 25 is connected, can be passed through the with inert impurities such as cyclic propylene carbonate, loaded inert gas sequentially sequentially switched cooler 13, in which the impurities are auskondensierbar and can be collected in a container 14. Downstream of the radiator 13, a cold trap 26 is arranged for not yet condensed gaseous impurities, to which an exhaust system 15 is connected.

From the bottom 23 of the stripping column 2 goes off a product line 27, through which the purified polyethercarbonate polyol is pumped by means of a pump 18 into a vented section 28. Duct container 29 can be transferred. The product line 27 is also equipped with a heater 9. In the product line 27, a three-way valve 30 is further arranged, from which a return line 31 goes off, which opens into the sump 11 of the evaporation device 1.

The preparation of a crude product to be purified with the device according to the invention was carried out in a continuously operated 60 l pressure reactor with gas metering device and product discharge tube, in which 4.7 kg propylene carbonate (cPC) and 200 ppm activated DMC catalyst (prepared according to WO 01 / 80994 AI, local example 6) were submitted. At 107 ° C. and 74 bar (absolute), the following components were metered in at the indicated metering rates with stirring (15 Hz): - propylene oxide with 6.41 kg / h

- Carbon dioxide at 2.6 kg / h

Mixture of glycerol / propylene glycol (85% by weight / 15% by weight) containing 0.69% by weight of DMC catalyst (not activated) and 170 ppm (based on the starter mixture) of H3PO ₄ at 0.26 kg /H. The reaction mixture was continuously withdrawn from the reactor via the product discharge tube so that the reaction volume of 27.4 L was kept constant. To complete the reaction, the reaction mixture was transferred to a tempered at 107 ° C after-reactor (tube reactor with a reaction volume 10.4 L). The resulting polyethercarbonate polyol (crude product) contains 8.4% by weight of cyclic propylene carbonate (cPC). The content of cyclic carbonate (which was formed as a by-product) in the context of the present invention is generally determined by the 'H-NMR resonance at 4.5 ppm, carbonate resulting from carbon dioxide incorporated in the polyether carbonate polyol (resonances at 5.1 to 4 , 8 ppm), unreacted PO with resonance at 2.4 ppm, polyether polyol (ie without incorporated carbon dioxide) with resonances at 1.2 to 1, 0 ppm, the optionally incorporated as a starter molecule 1.8 octanediol with a resonance at 1 , 6 to 1.52 ppm.

The molar fraction of the carbonate incorporated in the polymer in the reaction mixture is calculated according to formula (II) as follows, using the following abbreviations:

F (4,5) = area of resonance at 4.5 ppm for cyclic carbonate (equivalent to one H atom)

F (5, 1-4, 8) = area of resonance at 5.1-4.8 ppm for polyether carbonate polyol and a H atom for cyclic carbonate. F (2,4) = area of resonance at 2.4 ppm for free, unreacted PO

F (1.2-1.0) = area of resonance at 1.2-1.0 ppm for polyether polyol

F (1, 6-1.52) = area of resonance at 1.6 to 1.52 ppm for 1.8 octanediol (starter)

Taking into account the relative intensities, the following formula (II) for the polymer-bound carbonate ("linear carbonate" LC) in the reaction mixture was converted to mol%: (5, l - 4,8) - (4,5)

L C * 100 (Π)

F (5, l - 4,8) + F (2,4) + 0,33 * F (l, 2 - 1,0) + 0,25 * F (l, 6 - 1,52)

The weight fraction (in% by weight) of polymer-bound carbonate (LC) in the reaction mixture was calculated according to formula (III),

[(5, l - 4,8) - (4,5)] * 102

LC * 100% (III)

N where the value for Ν ("denominator" N) is calculated according to formula (IV):

N = [F (5,1-4,8) -F (4,5)] * 102+ F (4,5) * 102 + F (2,4) * 58 + 0,33 * F (l, 2-1, 0) * 58 + 0.25 * F (l, 6-l, 52) * 146

(IV)

The factor 102 results from the sum of the molar masses of CO ₂ (molar mass 44 g / mol) and that of propylene oxide (molar mass 58 g / mol), the factor 58 results from the molar mass of propylene oxide and the factor 146 results from the molar mass of the optionally used starter 1,8-octanediol.

The weight fraction (in% by weight) of cyclic carbonate (CC) in the reaction mixture was calculated according to formula (V),

F (4 5) * 102

CC '=' ^} * 100% (V)

N where the value for N is calculated according to formula (IV).

During operation of the cleaning device shown in FIG. 1, the crude product produced as described above, ie the polyether carbonate polyol loaded with production-related impurities, optionally after addition of different amounts of phosphoric acid (see Table 1) for stabilization, is transferred from the drum 4 via the heated supply line 5 pumped into the inlet 6 of the evaporator 1. To reduce the viscosity of the crude product this is already heated in barrel 4 to 50 ° C and required with powers of 2.1 kg / h to 5.5 kg / h (see Table 1) to the evaporation device 1. The falling-film evaporator is designed as a glass apparatus with an area of 0.5 m ² and is operated by means of a vacuum device not shown here at a pressure of 10 mbar.

In the evaporation device 1, during the passage of the crude product, part of the volatile impurities, in particular a part of the cyclic propylene carbonate, which is removed via the gas outlet line 12, condenses via the coolers 13 and is collected in the collecting vessel 14. Here, the first continuous cooler 13 is operated with a coolant temperature at 10 ° C and the sequentially downstream cooler 13 with a coolant temperature of -20 ° C.

The prepurified product collects in the sump 11 of the evaporation device 1, from where it is conveyed to a controllable via the three-way valve 16 share via the connecting line 3 of the stripping 2 and the other part via the return line 17 to the inlet 6 of the evaporation device 1. By using the return line 17, a part of the already prepurified product is again supplied to the cleaning via the evaporation device 1, whereby the cleaning performance increases. The prepurified product has a temperature of about 160 ° C at the end of the downcomer of the evaporator 1. In the evaporator 1, about 70% by weight of the low boilers contained in the crude product are separated in the present arrangement.

The prepurified product removed from the circuit via the connecting line 3 is fed to the head 21 of the stripping column 2. In this case, the connecting line 3 is heated by means of the heater 9 to about 100 ° C to prevent a large increase in viscosity by cooling the product. Immediately before the task on the head 21 of the stripping column 2, the prepurified product is heated by means of the heat exchanger 20 to about 160 ° C. The prepurified product passes through the stripping column 2 according to gravity, wherein the stripping column 2 mit- help the heating jackets 22 is operated essentially adiabatic. Serve this purpose at several points with the heating jackets 22 coupled temperature sensor 22a.

The stripping column 2 is operated countercurrently with a heated to 160 ° C and fed via the gas inlet line 24 nitrogen flow. In the nitrogen stream flowing in the direction of the head 21, the volatile constituents accumulate and are fed via the gas outlet line 25 to the coolers 13, in which the volatile compounds, in particular the cyclic propylene carbonate, are condensed and collected in the collecting vessel 14. Here, the first continuous cooler 13 is operated at a temperature of 10 ° C and the downstream cooler with a temperature of -20 ° C. At the sampling point 19 arranged in the inlet of the cold trap 26, the inert gas stream can still be checked for any impurities before it is removed from the cycle via the exhaust air system 15 or else returned to the circuit via a compression system.

In the bottom 23 of the stripping column 2, the purified product, which has passed through the stripping column 2, and which is transferred via the product line 27 by means of the pump 18 in the product container 29 collects. By means of the provided in the product line 27 three-way valve 30, a portion of the product stream can be diverted and transferred via the return line 31 back into the sump 11 of the evaporation device 1. During the startup period of the cleaning device, the entire product stream discharged in the sump 23 via the product line 27 is returned via the return line 31 to the sump 11 of the evaporation device 1 until the desired product purity is achieved. This is checked by means of the sampling point 19 provided in the product line 27.

The residence time of the prepurified product in the bottom 11 of the evaporation device 1 is about 10 minutes and in the bottom 23 of the stripping column 2 about 6 minutes.

Experiments were carried out in the plant described, wherein the evaporation device 1, the connecting line 3 to the stripping column 2 and the inert gas (nitrogen) were adjusted to 160 ° C. The evaporation device 1 ran at an operating pressure of 10 mbar, the stripping column 2 at 80 mbar. Table 1 summarizes the relevant process parameters and the final concentrations of cyclic propylene carbonate cPC in the final purified product. Table 1 :

phosphoric acid 1) (nitrogen) in the end product

Stripping column 2

1 5.5 kg / h 2.275 kg / h 55 ppm

2 61 ppm 4.7 kg / h 2.275 kg / h 17 ppm

3 100 ppm 2.1 kg / h 2.275 kg / h 17 ppm

4 100 ppm 4.2 kg / h 2.275 kg / h 20 ppm

5 100 ppm 5.2 kg / h 2.275 kg / h 24 ppm

The experiments prove that the required maximum value of 100 ppm cPC in the end product can be reliably exceeded by the method according to the invention. Addition of small amounts of phosphoric acid (Examples 2 - 5) causes a stabilization of the polyethercarbonate polyol, so that in this way significantly lower residual concentrations of cPC in the final product can be achieved than without the addition of phosphoric acid (Example 1).

Reference sign list:

(1) Evaporator;

(2) stripping column

(3) Connecting line

(4) barrel

(5) Supply line

(6) inlet

(7) Ventilation

(8) shut-off valve

(9) heating

(10) heating

(10a) feed

(10b) expiration

O D swamp

(12) Gas outlet pipe

(13) cooler

(14) Collecting container

(15) Exhaust system

(16) Three-way valve

(17) Return line

(18) Pump

(19) Sampling point

(20) Heat exchanger

(21) head

(22) Heating jacket

(22a) Temperature sensor

(23) swamp

(24) Gas inlet pipe

(25) Gas outlet pipe

(26) Cold trap

(27) Product line

(28) Ventilation

(29) Product container

(30) Three-way valve

(31) Return line

Claims

Patent claims:

Cleaning device for polycarbonate polyols, in particular for separating cyclic alkylene carbonates, comprising an evaporation device (1) provided with a heater (10) with an inlet (6) arranged on the top and a sump (11) and a stripping column connected downstream to the evaporation device (1). (2) with a head (21) and a sump (23), a feed line (5) for the polycarbonate polyol to be cleaned opening into the inlet (6) of the evaporation device (1) and a gas outlet line (12) from the evaporation device (1). ) and a connecting line which opens into the head (21) of the stripping column (2) and is equipped with a pump (18), and a gas inlet line (24) for an inert gas opens into the bottom (23) of the stripping column (2) and from From the bottom (23) of the stripping column (2) there is a product line (27) for the purified polycarbonate polyol and from the top (21) of the stripping column (2) there is a gas outlet line (25).

Cleaning device according to claim 1, characterized in that the gas outlet line (12) of the evaporation device (1) and/or the gas outlet line (25) of the stripping column

(2) each open into a cooling device (13), in which impurities converted into the gaseous state and removed via the gas outlet line (12, 25) can be condensed, in particular cyclic alkylene carbonates.

Cleaning device according to claim 1 or 2, characterized in that the supply line (5), the connecting line

(3), the gas inlet line (24) and/or the product line (27) are equipped with a heater (9).

4. Cleaning device according to one of the preceding claims, characterized in that a three-way valve (16) is arranged in the connecting line (3), from which a return line (17) provided, if desired, with a heater (9) and / or a pump (18). that goes into the supply line

(5) or opens into the inlet (6) of the evaporation device (1).

Cleaning device according to one of the preceding claims, characterized in that a three-way valve (30) is arranged in the product line (27), from which a return line (31) which is optionally provided with a heater (9) and/or a pump (18) leaves, which opens into the evaporation device (1), in particular into the sump (11) of the evaporation device (1).

6. Cleaning device according to one of the preceding claims, characterized in that a pump (18) is provided in the feed line (5) and/or the product line (27).

7. Cleaning device according to one of the preceding claims, characterized in that the evaporation device (1) is designed as a natural circulation, forced circulation, falling film, thin film or kettle evaporator, preferably as a falling film or thin film evaporator, the supply line (5) opens into the inlet (6) of the evaporation device (1) and the connecting line (3) and the gas outlet line (12) branch off from the sump (11) of the evaporation device (1).

8. Cleaning device according to one of the preceding claims, characterized in that the evaporation device (1) is coupled to a vacuum device, which is in particular designed such that the evaporation device (1) can be operated at a pressure of 100 mbar or below, preferably at 5 to 100 mbar, preferably at 50 mbar or below, more preferably at 25 mbar or below, particularly preferably at 10 mbar or below.

9. Cleaning device according to one of the preceding claims, characterized in that the stripping column (2) is coupled to a vacuum device, which is in particular designed such that a pressure of 150 mbar or below is set in the head (21) of the stripping column (2). can be, preferably 100 mbar or below, preferably 80 mbar or below.

10. Cleaning device according to one of the preceding claims, characterized in that the stripping column (2) is provided with a heating jacket (22) which enables a substantially adiabatic operation of the stripping column (2).

11. Cleaning device according to one of the preceding claims, characterized in that the stripping column (2) is filled with packings and / or packings and / or equipped with trays, Raschig Super rings in particular being used as packings.

12. A method for cleaning polycarbonate polyols with a cleaning device comprising an evaporation device (1) provided with a heater (10) with an inlet (6) arranged on the top and a sump (11) and a stripping column connected downstream to the evaporation device (1). (2) with a head (21) and a sump (23), in particular with a cleaning device according to one of claims 1 to 11, the method comprising the following steps: g) feeding the polycarbonate polyol to be cleaned into the inlet (6) of the evaporation device (1) through a feed line (5) opening into it; h) in the evaporation device (1) transferring part of the impurities into the gas phase and removing the gaseous impurities via a gas outlet line (12), a partially purified polycarbonate polyol being obtained in the bottom (11) of the evaporation device (1); i) transferring the partially purified polycarbonate polyol from the bottom (11) of the evaporation device (1) into the top (21) of the stripping column (2) through a connecting line (3) opening into it, in particular by means of a pump (18); j) Removing a further part of the impurities from the partially purified polycarbonate polyol by stripping in countercurrent through an inert gas stream introduced into the bottom (23) of the stripping column (2) via a gas inlet line (24) and opposite to the flow direction of the polycarbonate polyol, the impurities being in the Gas phase is transferred and transported with the inert gas stream; k) removing the impurities with the inert gas through a gas outlet line (25) extending from the top (21) of the stripping column (2);

1) Removing the purified polycarbonate polyol via a product line (27) departing from the bottom (23) of the stripping column (2).

Method according to claim 12, characterized in that nitrogen, carbon dioxide and/or water vapor is used as the inert gas.

Method according to claim 12 or 13, characterized in that the impurities to be removed include cyclic alkylene carbonates, in particular cyclic propylene carbonate, the proportion of cyclic alkylene carbonates in the purified polycarbonate polyol being preferably less than 100 ppm.

Method according to one of claims 12 to 14, characterized in that phosphoric acid is added to the polycarbonate polyol to be cleaned before or during cleaning, in particular in a concentration of 10 to 1000 ppm, based on the polycarbonate polyol to be cleaned, in particular 15 to 500 ppm.